JPS6374117A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve film strength of a magnetic layer and to enhance running stability by providing multi-layered structure consisting of >=2 layers on a thin ferromagnetic metallic film layer and incorporating carbon into at least one layer of the thin ferromagnetic metallic film layers. CONSTITUTION:The thin ferromagnetic metallic film layer as the magnetic layer has the multi-layered structure consisting of >=2 layers which contain Co as the essential component. Such magnetic layer is preferably the aggregate of the particles having the columnar crystalline structure inclined with the normal of the main plain of the substrate. The carbon is incorporated in the form of the polymer of an org. material into at least one layer of the multi- layered magnetic layer and said polymer exists in the magnetic layer, more particularly so as to fill the spacings between the columnar particles and columnar particles forming the magnetic layer. Such org. material polymer is as dense as to prevent the contact of the columnar particles of the magnetic layer with O2 molecules in the air and the atomic ratio of the carbon/metal in the layer contg. such carbon is 10<-8>-10<-2>. Output and coercive force decrease when said atomic ratio deviates from the above-mentioned range.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, particularly a metal thin film type magnetic recording medium.

Prior art and its problems As magnetic recording media for video, audio, etc., media having a metal thin film type magnetic layer are being actively developed because of their compactness when wound into tapes.

Due to its characteristics, the magnetic layer of such a metal thin film type medium is made of a Co-based, Co-Ni-based, etc. material formed by a so-called oblique evaporation method, in which the evaporation is performed at a predetermined angle to the normal to the substrate. Membranes are preferred.

Such a magnetic recording medium in which the magnetic layer is composed of a ferromagnetic metal thin film layer is advantageous over a coating-type magnetic recording medium because it does not contain a binder, can be easily made thin, and has a large saturation magnetization. However, on the other hand, in non-binder type magnetic recording media, the magnetic layer is formed by methods such as electroplating, electroless plating, sputtering, vacuum evaporation, and ion blating, and does not contain a binder. time, e.g. recording and reproducing magnetic signals,
During erasing, the magnetic layer is likely to be scraped off or destroyed by friction caused by high-speed relative motion with the magnetic head. In addition, the surface of the magnetic layer of non-binder type magnetic recording media is prone to corrosion, and as corrosion progresses, practical properties such as head touch and wear resistance tend to deteriorate, and the electromagnetic conversion properties also tend to suffer. . Furthermore, head contact is poor due to curling or cupping of the medium.
Output fluctuations occur.

A method of applying a lubricant to the surface of the magnetic layer as a means of reducing the impact and friction experienced by magnetic recording media (Japanese Patent Publication No. 39 Sho.
-25246).

In addition, as a means to continuously supply lubricant to the surface of the magnetic layer, a lubricant layer (mainly composed of a liquid or semi-solid lubricant and an organic binder) is provided on the surface of the magnetic recording medium opposite to the magnetic layer.
Method for forming back coat layer (Special Publication No. 57-297
No. 69) has been proposed. In this method, when the magnetic recording medium is wound into a roll, the lubricant that oozes from the back coat layer on the back side transfers to the surface of the magnetic layer, making it possible to supply lubricant to the surface of the magnetic layer. , it is said that this increases the durability of the magnetic layer (to the extent of scratches and peeling), and also makes it possible to easily respond to changes in the dynamic fly coefficient.

However, in the method described in Japanese Patent Publication No. 39-25246, the lubricant is removed by a magnetic head, etc., so the lubricant action does not last long, and the effects of rust prevention and durability cannot be expected. .

Furthermore, as in the method described in Japanese Patent Publication No. 57-29769, simply adding a lubricant to the back coat layer without forming a top coat layer on the surface of the magnetic layer,
The friction between the magnetic layer surface and the magnetic head is still large;
It is easy to cause poor running, and satisfactory results cannot be obtained in terms of corrosion resistance and rust prevention effect. Furthermore, when the lubricant of the back coat layer is back-transferred to the magnetic layer that is not top-coated, for example, when oxygen is not introduced in the vapor-deposited film (metallic film that does not contain oxygen: Japanese Patent Publication No. 57-29769
Although it is not noticeable in the case of the current standard method of introducing oxygen (oxygen-containing metal film), the film becomes unstable, resulting in a decrease in output and clogging, or a loss of images. , or the frictional resistance did not decrease sufficiently and remained large, and sometimes the film was scraped off or destroyed.

Furthermore, in contrast to the method of containing a lubricant in the back coat layer, a method of applying a lubricant to the top coat layer can be easily considered. However, with this method, although the friction is reduced, it is only temporary and does not continue, and only magnetic recording media with significantly inferior rust prevention, corrosion resistance, durability, etc. can be obtained.

Furthermore, in order to improve durability and electromagnetic conversion characteristics, proposals have been made to make the ferromagnetic metal thin film layer have a multilayer structure of two or more layers (Japanese Unexamined Patent Publication No. 54-141608, Publication No. 56-26892, JP-A No. 57-130228, etc.).

However, in this case as well, as described above, head touch deteriorates due to curling or cupping of the medium, resulting in output fluctuations.

As mentioned above, at present, a technology that has good runnability, durability, and ferromagnetic thin film strength, has no disadvantages in terms of electromagnetic conversion characteristics, and does not cause curling or cupping of the medium has not yet been realized. .

■ Purpose of the Invention The purpose of the present invention is to provide a medium with good running properties, less cracking or chipping of the magnetic layer due to running, less head wear and dropouts, and improved curling or cupping of the medium. An object of the present invention is to provide a metal thin film type magnetic recording medium with good electromagnetic conversion characteristics.

■Disclosure of invention Such objects are achieved by the invention described below.

That is, the present invention provides C on a plastic film substrate.
The ferromagnetic metal thin film layer has a multilayer structure consisting of two or more layers, and at least one of the ferromagnetic metal thin film layers contains carbon. This is a magnetic recording medium characterized by:

■Specific structure of the invention Hereinafter, five specific configurations of the present invention will be explained in detail.

The ferromagnetic metal thin film layer as the magnetic layer in the present invention is Co
It has a multilayer structure consisting of at least two layers, including as a main component.

Such a magnetic layer is usually preferably an aggregate of particles having a columnar crystal structure tilted with respect to the normal to the main surface of the substrate. This improves electromagnetic conversion characteristics.

In the present invention, at least one of the multilayer magnetic layers contains carbon in the form of an organic polymer. Such an organic polymer exists in the magnetic layer, particularly in the space between the columnar particles forming the magnetic layer. Such an organic polymer is so dense that the columnar particles of the magnetic layer and the 02 molecules in the air cannot come into direct contact with each other.

The carbon/metal atomic ratio in such a carbon-containing layer is between 10-8 and 10-2.

If the carbon/metal ratio is out of the above range, the output and coercive force will decrease.

Further, the effect of improving corrosion resistance cannot be obtained.

The carbon/metal atomic ratio in the magnetic layer can be easily obtained by identifying the composition of the magnetic layer by Auger spectroscopy or SIMS.

tp +: +n RE 'n
+, + l'M 4% j+ /J,% P
I I) -#, -1:f4 1. The layer containing carbon may be any layer, but it is usually preferable to be the top layer, and furthermore, all the layers contain carbon, and the layer as a whole , the carbon/metal atomic ratio is preferably 10-8 to 10-2.

Various organic polymers are possible, but those containing C and H are particularly preferred.

In this case, the C/H atomic ratio is preferably about 6 per layer.

The method for incorporating the organic polymer into the magnetic layer as described above may be carried out according to the method shown below.

3 and 4 illustrate an example of the media manufacturing apparatus of the present invention. FIG. 3 shows a vapor deposition apparatus 11 that forms a magnetic layer while incorporating 41 components.
FIG. 4 also shows an organic polymerization processing apparatus 20 (a plasma processing apparatus is shown in FIG. 4 as an example).

In the vapor deposition apparatus 11, the substance evaporated from the evaporation source 16 is deposited on the substrate in an ill-reduced manner from a high incidence angle θmax (position b) to a low incidence angle θm1n (position C) regulated by the shielding plate 17. Then, a magnetic layer is formed.

In the present invention, when forming the magnetic layer, an organic gas is introduced from the nozzle 15 located between 5 and 0, and the organic substance is incorporated into the magnetic layer.

Examples of organic substances include those that become gas under reduced pressure of about 10-5 Torr, such as (A) methane, ethane, propane, butane, pentane,
Ethylene, propylene, butene, butadiene, acetylene, methylacetylene, benzene, styrene, and other saturated or unsaturated hydrocarbons; (B) Fluoromethane, difluoromethane, trifluoromethane, difluoroethane, tetrafluoroethane, and other saturated or unsaturated hydrocarbons; (C) Tetrafluoromethane, hexafluoroethane, octafluoropropane, octafluorocyclobutane, tetrafluoroethylene, hexafluoropropylene, and other saturated or unsaturated fluorinated carbons, (D) Others , methyl methacrylate, acrylic acid,
Examples include vinyl chloride and vinylidene chloride.

Usually, one of these (A) to (D) is used alone as the raw material gas, but two or more types may be used in combination.

Further, if necessary, trace components such as nitrogen, oxygen, boron, and phosphorus can be added to the raw materials.

Among these, methane, ethane with carbon number of 3 or less,
Preferably, ethylene, acetylene, propane, propylene, methylacetylene, tetrafluoromethane, tetrafluoroethylene, etc. are used.

These raw material gases may be introduced from any position between b and c shown in FIG. 3 in order to bring them into contact with the deposited particles forming the magnetic layer.

The flow rate of the raw material gas may be appropriately determined depending on the volume of the vacuum chamber, etc., but is usually about 10 to 110003 CC.

Note that the above-mentioned introduction of the organic substance can be similarly applied to the case where the magnetic layer is formed by a vacuum film-forming method other than vapor deposition, such as ion blasting or sputtering.

The organic substances incorporated into the magnetic layer during the formation of the magnetic layer in this way are then polymerized by an organic substance polymerization treatment apparatus 20 as shown in FIG. Although the polymerization means installed in the polymerization processing apparatus 20 is not particularly limited, the following method is usually used.

(1) A method of polymerizing in a plasma atmosphere using plasma.

(2) A method of polymerizing by irradiation with radiation such as electron beams and ultraviolet rays.

However, when using the radiation described in (2) above, the organic substances incorporated into the planar magnetic layer are limited to those having multiple bonds such as ethylene, acetylene, propylene, butadiene, styrene, and benzene.

FIG. 4 shows an apparatus for polymerizing organic matter incorporated into a magnetic layer in a plasma atmosphere using the method (1) above.

The plasma atmosphere is, for example, N2.02, N2, Ar
, He, Ne, etc., and is created by discharge plasma of these gases.

To outline the principle, when a gas is kept at a low pressure and an electric field is applied, the free electrons present in a small amount in the gas are accelerated by the electric field because the intermolecular distance is much larger than at normal pressure.
Obtain a kinetic energy (electron temperature) of 10 eV.

When these accelerated electrons collide with atoms and molecules, they disrupt atomic and molecular orbits and dissociate them into chemical species that are unstable under normal conditions, such as electrons, ions, and neutral radicals.

The disintegrated electrons are again accelerated by the electric field, causing other atoms and molecules to disintegrate, and this chain reaction quickly turns the gas into a highly ionized state. And the dough is called plasma gas.

Gas molecules have fewer chances of collision with electrons, so they do not absorb much energy and are kept at a temperature close to room temperature.

A system in which the kinetic energy of electrons (electron temperature) and the thermal motion of molecules are separated is called a low-temperature plasma, in which chemical species undergo acidic chemical reactions such as polymerization while remaining relatively intact. In manufacturing the magnetic recording medium of the present invention, this situation is used to polymerize the organic matter incorporated into the magnetic layer by exposing it to a plasma atmosphere. Note that since low-temperature plasma is used, there is no heat Hp applied to the substrate, magnetic layer, etc.

In FIG. 4, a processing gas is supplied to the reaction vessel R from a processing gas source 21 or 22 via mass flow controllers 23 and 24, respectively. When separate gases are supplied from the waste sources 21 or 22, they are mixed in the mixer 25 and then supplied.

The process gases each have a flow rate range of 1-250 mIL/min.

Inside the reaction vessel R, a film-shaped object, for example, having a magnetic layer incorporating an organic substance on a substrate is let out from a take-out roll 31 and wound up by a take-up roll 30 . During this time, the organic matter incorporated into the magnetic layer is polymerized.

Further, to explain the polymerization treatment apparatus 20 in detail, electrodes 27 and 57 are provided which face each other with the object to be treated in between.One electrode 27 is connected to a frequency variable power source 26, and the other electrode 57 is grounded at 28.

Furthermore, a vacuum system for evacuating the inside of the reaction vessel R is provided, and this is connected to the liquid nitrogen trap 11.
1. Oil rotary pump 112 and vacuum controller 113
including. These vacuum systems operate at a pressure of 0.01~
Maintain a vacuum level of 10 Torr.

In the operation, the inside of the reaction volume eR is first heated to 10' T.
The inside of the container is evacuated by an oil rotary pump until the temperature is below o r r, and then the processing gas is supplied in a mixed state into the container at a predetermined flow rate.

At this time, the vacuum inside the reaction vessel is 0.01 to 10 Torr.
It is managed within the range of r.

When the transfer speed of the object to be processed and the flow rate of the processing gas are stabilized, the variable frequency power source is turned on. In this way, the object being transferred is subjected to plasma treatment.

In such plasma processing, in the present invention, N2.02, N2, A as described above is used as the plasma gas.
A gas such as r, Ne, or He is used.

Usually, one type of these dregs is used alone, but two or more types may be mixed and used as necessary.

The plasma processing conditions are an indoor pressure of 0.01 to 10 Torr.
r, frequency 10, N2~2GH2,', pressure 0.5~
The stiffness condition is estimated to be about 5 KW, and is determined experimentally for each manufacturing device because it affects the film quality of the magnetic layer.

By the way, when a method of irradiating radiation is used instead of such a method using plasma when polymerizing the organic substance incorporated into the magnetic layer, various known apparatuses may be used instead of the apparatus shown in FIG. A radiation irradiation device is used.

In that case, active energy rays used for polymerization include, for example, electron beams using a radiation accelerator as a source, γ-rays using a Co60 source, β-rays using a 5r90 source, and X-ray generators IIi! X-rays or ultraviolet rays are used as a source.

In particular, as an irradiation source, it is advantageous to use radiation using a radiation accelerator from the viewpoints of controlling the absorbed dose, introducing it into the manufacturing process line, and shielding ionizing radiation.

As for the radiation characteristics used, from the perspective of penetrating power, it is recommended to use an acceleration voltage of 100 to 750 KV, preferably 150 to 300 V, and irradiate the radiation so that the absorbed LIT amount is 0.5 to 20 megarads. It's convenient.

During polymerization, a low-dose type radiation accelerator (Electro Curtain System) manufactured by Energy Sciences, Inc. in the United States was introduced into the tape processing line, and the secondary X, 1! This is extremely advantageous for shielding, etc.

Of course, a van de Graaf type accelerator, which has been widely used as a radiation accelerating material, may also be used.

In addition, during radiation crosslinking, it is important to irradiate radiation in an inert gas flow such as N2 gas or He gas.
Irradiating radiation in the air is extremely disadvantageous because it inhibits the radicals generated in the organic matter due to 03 etc. generated by radiation irradiation during polymerization from working effectively on the polymerization reaction. Therefore, the atmosphere in the area where the active energy rays are irradiated is particularly N2 with a maximum oxygen concentration of 5%.
It is important to maintain an atmosphere of an inert gas such as , He, or Co2.

By polymerizing the organic substance incorporated into the magnetic layer in this way, the resulting medium is extremely less prone to curling and cupping.

This results in stable output and excellent corrosion resistance and running durability.

Further, the ferromagnetic metal thin film layer used in the present invention has a composition mainly composed of Co, containing O, and further containing Ni and/or Cr as necessary.

That is, in a preferred embodiment, it may be made of Cof... or may be made of Co and Ni. When Ni is included, the weight ratio of Co/Ns is preferably 1.5 or more.

Furthermore, Cr may be contained in the ferromagnetic metal thin film layer.

In such cases, Cr/Co or Cr/(Co
+N i ) weight ratio is 0.1 or less, especially 0.001 to
It is preferably 0.1, more preferably 0.005 to 0.05.

Furthermore, it is preferable that the ferromagnetic metal thin film contains zero.

The average amount of oxygen in the entire layer in the ferromagnetic metal thin film is an atomic ratio, particularly the atomic ratio of O/(Co or Co+N i ), and the average oxygen amount CI in the top layer is about 0.1 to 0.5, preferably It is about 0.1 to 0.4.

When the average oxygen content CI' is less than 0.1, corrosion resistance, runnability,
Insufficient in terms of cracks, scratches, etc. in the magnetic layer, 0
．． If it exceeds 5, the surface oxide layer increases, causing problems such as a decrease in output due to spacing with the head.

Then, the oxygen concentration C2 near the interface with the bottom plastic film, especially 0/(Co or Co+N i )
The atomic ratio is determined by the oxygen concentration C1 near the surface opposite to the top layer plastic film, especially O/(Co or Co+N
i) The value C2/C1 divided by the atomic ratio is 0.3 or less,
More preferably, it is 0.15 or less.

In this case, these oxygen concentrations can be measured by performing Auger spectroscopy, SIMS (secondary ion mass spectrometry), etc. while ion milling or ion etching the ferromagnetic metal thin film with Ar or the like.

That is, while performing ion etching, 0, Co,
Ni, etc. are counted and their profiles in the film thickness direction are compared.

Then, 0/(Co or Co+Ni) on the surface of the ferromagnetic metal thin film on the opposite side to the plastic film is defined as CI.

In addition, for the bottom layer, etching is performed down to the plastic film, and the O/
(C.

or Co+N i) as C2.

Ion etching and Auger spectroscopy or SIM
S may be measured by a conventional method.

In this way, by relatively increasing the oxygen concentration on the surface of the top layer, the coercive force Hc increases, and by decreasing the oxygen concentration in the bottom layer, the maximum residual magnetic flux φ and the squareness ratio S0 increase. t'%<, resulting in a magnetic layer with extremely good electromagnetic conversion characteristics.

Furthermore, in the ferromagnetic metal thin film layer described in F, the oxygen concentration C3 near the interface between the uppermost layer and the uppermost layer of the adjacent layer, especially the O/(Co or Co+Ni) atomic ratio, is opposite to that of the uppermost plastic film. Oxygen concentration CI near the side surface,
In particular, the value C3/Cr divided by the atomic ratio of 0/(Co or Co+N i ) is o, 1 to 3.0, more preferably 0.
It is preferable that it is 2-2.0.

In this case, the O/(Co or Co+Ni) atomic ratio CI on the surface of the ferromagnetic metal thin film on the side opposite to the plastic film can be measured in the same manner as described above. Regarding the oxygen concentration C8 near the interface with the top layer of the layer adjacent to the top layer, O/(Co or Co+Ni) is calculated from the count during etching corresponding to the film thickness of the top layer, and this is calculated as C3. And it is sufficient. However, in each layer, under normal film forming conditions, the oxygen concentration is highest on the opposite side of the film substrate. For this reason, when counting 0 while performing ion etching, the maximum value within the film is usually set to C3.
And it is sufficient.

By relatively increasing the oxygen concentration C8 on the surface of the top layer in this way, the coercive force Hc becomes high, and the oxygen concentration in the area below the surface of the top layer to the vicinity of the layer adjacent to the top layer increases. By making C1 relatively lower than the above C1,
The maximum residual magnetic flux φr and the squareness ratio S0 are increased, resulting in a magnetic layer with extremely good electromagnetic conversion characteristics. therefore,
A signal with a relatively shallow magnetic field having a center frequency of about 5 MHz is effectively held in the uppermost layer.

In addition, the relationship between the oxygen concentration C3 near the interface with the top layer of the layer adjacent to the top layer and the above C is as described above.
By making C1 relatively high in the range of o, i to 3.0, the coercive force Hc in this part increases,
In addition, by making the oxygen concentration of the layer adjacent to the top layer below the interface with the top layer relatively lower than that of C3 above, the maximum residual magnetic flux φ and the squareness ratio SQ are increased, and the electromagnetic conversion characteristics This results in an extremely good magnetic layer. Therefore, a signal with a relatively deep magnetic field with a center frequency of about 0.75 MHz is effectively retained in the layers adjacent to the top layer and below.

As for the relationship between CI and C3, as mentioned above, C
When 3/C+ is 0.1 to 3.0, the magnetic layer has an excellent magnetic layer with the best balance in electromagnetic conversion characteristics, corrosion resistance, etc.

The atomic ratio C2 of 0/(Co or Co+Ni) near the surface is generally 0.2 to 0.7, preferably 0.3 to 0.
．． It is 6.

Therefore, 1, 0/(Co or C near the film interface)
o+N i ) Atomic ratio C2 is 0.06 to 0.21. Preferably it is 0.09 to 0.18.

Further, the 0/(Co or Co+N i ) atomic ratio C3 in the vicinity of the top layer of the layer adjacent to the top layer is 0.07 to 0.6,
Preferably it is 0.1 to 0.5.

Furthermore, O/(Co or Co+N
i) The average atomic ratio C,11 is preferably 0.1 to 0.5, more preferably 0.1 to 0.4. Further, the average atomic ratio C211 of 0/(Co or Co+Ni) in the entire bottom layer is 0.5 or less, more preferably 0.
It is preferably 3 or more -F. Also, 0/(Co or Co+N i ) for the entire layer adjacent to the top layer is 0
．． It is preferably 5 or less, more preferably 0.3 or more.

At this time, electromagnetic conversion characteristics, corrosion resistance, running durability, magnetic film strength, etc. become extremely good.

In this case, in the case of a multilayer structure with three or more layers, O/(Co or Co+Ni) in each layer as a whole is generally
It is 0.5 or less, preferably 0.3 or less.

Regarding the oxygen concentration profile in the thickness direction of a ferromagnetic metal thin film, there is usually a peak of oxygen content 4r at least at the interface between the uppermost layer and the layer adjacent to the lowermost layer.

Note that the ferromagnetic metal thin layer 11Q usually has only two layers, but it can also have three or more layers, especially 3 to 5 layers, if necessary.

In addition, such a ferromagnetic metal thin film may further contain other trace components, especially transition elements such as Fe, Mn, V, Zr,
Nb, Ta, Ti.

Zn, Mo, W, Cu, etc. may be included.

In a preferred embodiment, such a ferromagnetic metal thin film layer is composed of an aggregate of columnar crystal grains mainly composed of Co as described above.

In this case, the total thickness of the ferromagnetic metal thin film layer is 0.05
~0.5 μm, preferably 0.07 to 0.3 μm.

There is no particular restriction on the ratio of the thickness of each layer of such a thin ferromagnetic metal 11Q layer, but for example, in the case of a two-layer structure, the ratio of the thickness of the upper layer and the lower layer is preferably about 0.1 to 10, More preferably 0.2 to 0.9, still more preferably 0.4 to
0.9 is preferred.

The columnar crystal grains have a length spanning almost the entire thickness direction of each layer, and the minimum angle in the longitudinal direction with respect to the normal to the principal surface of the substrate is preferably 20 to 90 degrees in the uppermost layer. is preferably in the range of 20 to 50 degrees, and preferably 50 degrees or less in the bottom layer, more preferably in the range of 0 to 40''.

In this case, in each intermediate layer in a structure of three or more layers, the inclination angle of the columnar crystal grains with respect to the normal to the main surface of the substrate is
Usually, it is sufficient that the angle is within the range of inclination angle between the top layer and the bottom layer, and there is no particular restriction.

In this case, the directions of inclination of the crystal grains of each adjacent magnetic layer with respect to the normal to the main surface of the substrate may be the same direction in the length direction of the medium, but preferably they are in opposite directions. preferable.

The direction of the inclination of the crystal grains is schematically illustrated using a two-layer structure as shown in FIGS. 1 and 2.

In FIGS. 1 and 2, a magnetic recording medium 1 has a ferromagnetic metal thin film lower layer 3 and a ferromagnetic metal thin film upper layer 4 on a base 2. As shown in FIGS. Then, the ferromagnetic metal thin film lower layer part 3
The direction of inclination of the lower layer crystal grains 5 in the ferromagnetic metal thin film upper layer section 4 and the direction of inclination of the upper layer crystal grains 6 in the ferromagnetic metal thin film upper layer section 4 are opposite directions in the longitudinal direction a of the medium in FIG. In the figure, the length direction a of the medium is the same direction.

Further, a top coat layer 7 may be provided on the surface of the ferromagnetic metal thin film upper layer portion 4 opposite to the substrate 2, and a back coat layer 8 may be provided on the surface of the substrate 2 on which the magnetic layer is not provided. good.

In the present invention, the crystal grains may have either the crystal grain inclination shown in FIG. 1 or FIG. 2, but those having the crystal grain inclination shown in FIG. 1 are preferable.

Note that oxygen exists in the form of a compound on the surface of the columnar crystal grains in the surface portion.

Moreover, it is preferable that the short axis of the crystal grain has a length of about 50 to 500 grains.

In this way, by forming the ferromagnetic metal thin film layer into a multilayer structure, the length of the columnar crystal grains becomes small, so that the film strength of the ferromagnetic metal thin film layer is improved.

In addition, the columnar crystal grains in the top layer are
If the magnetic field has an inclination of 90 degrees, and particularly an inclination of 50 degrees or more, for example, a signal having a center frequency of about 5 MHz and having a relatively shallow magnetic field can be effectively retained in the uppermost layer.

In addition, the columnar crystal grains in the bottom layer are at an angle of 50° to the normal to the main surface of the substrate.
If it has the following inclination and stands up against the base, for example, the center frequency is 0.75 with a relatively deep magnetic field.
Signals on the order of MHz can be effectively held in a lower layer region such as the lowest layer.

Furthermore, as mentioned above, by increasing the oxygen concentration in the top layer, oxides such as Co and Ni, which have excellent wear resistance, are formed in the top layer, which has a synergistic effect with the multilayer structure and carbon content. Accordingly, the film strength of the ferromagnetic metal thin film layer becomes higher.

The material of the substrate used in the magnetic recording medium of the present invention is not particularly limited as long as it is a non-magnetic plastic, but usually polyethylene terephthalate, polyethylene 2.6
- Polyester such as naphthalate, polyamide, polyimide, polyphenylene sulfide, polysulfone,
Fully aromatic polyester, polyetheretherketone,
Polyether sulfone, polyetherimide, etc. are used.

The thickness of the substrate is not particularly limited and may be about 5 to 20 μm, preferably about 8 μm or less, particularly about 5 to 7 μm.

This is because with a diameter of 8 μm or less, the objectives such as miniaturization of the medium and long-time recording can be achieved. However, if this thickness becomes too thin, the effect of increasing the film strength by making the magnetic layer have a multilayer structure as described above is canceled out, and problems such as running performance, decreased output, and head wear occur.

Further, the effect of improving electromagnetic conversion characteristics by forming a multilayer structure of ferromagnetic metal thin film layers according to the present invention becomes more noticeable when the thickness of the substrate is made thinner.

For example, taking a two-layer structure as an example, when the thickness of the substrate is 10 μm, the electromagnetic conversion characteristics are improved by changing the ferromagnetic metal thin YA layer from the conventional single-layer structure to the two-layer structure of the present invention. The signal in the low frequency range of .75 MHz is about +6 (dB), and the signal in the high frequency range of 5 MHz is about +6 (dB), but when the thickness of the base is 7 μm, the improvement is 0.
．． For a signal in a low frequency region of 75 MHz, it is about +6 (dB), which is equivalent to the case of a base J of 510 μm, but for a signal in a high frequency region of 5 MHz, it increases to about +7.5 (dB).

In this way, the reason why the electromagnetic conversion characteristics of a 7 μm thick base are significantly improved compared to that of a 10 μm thick base is that by increasing the base thickness from 10 μm to 7 μm, the head touch due to insufficient base rigidity deteriorates rapidly, and the 5 MHz This effect is more significant in high frequency ranges such as, and it is in such cases that the effects of the present invention are manifested.

In the present invention, the magnetic layer is preferably formed by a so-called oblique vapor deposition method.

In this case, the minimum angle of incidence of the deposited material with respect to the substrate normal is:
50° or less when the bottom layer is installed, 20 to 90° when the top layer is installed, and 20 to 50° when the middle layer is installed in a structure with three or more layers.
It is preferable that

When the minimum incident angle deviates from the above-mentioned incident angles, the electromagnetic conversion characteristics deteriorate.

Further, although two or more magnetic layers may be successively formed in one step, it is usually preferable to perform each layer in a vapor deposition step.

In this way, by dividing the magnetic layer into each layer, the direction of inclination of the magnetic columnar crystal grains with respect to the normal to the substrate can be made to face each other in the length direction of the medium between adjacent layers, as described above. direction.

With such a magnetic layer configuration, the electromagnetic conversion characteristics are extremely good.

The vapor deposition atmosphere is usually an inert atmosphere such as argon, helium, or vacuum, and an atmosphere containing oxygen gas.
The pressure may be approximately -5 to 10'Pa, and the deposition distance, substrate conveyance direction, structure and arrangement of cans and masks, etc. may be the same as known conditions.

Then, a metal oxide film is formed on the surface by vapor deposition in an oxygen atmosphere. Note that the oxygen gas partial pressure at which metal oxides are formed can be easily determined through experiments.

Note that various oxidation treatments can be performed to form a metal oxide film on the surface.

Applicable oxidation treatments include the following.

1) Dry process a, energetic particle process As described in Japanese Patent Application No. 76,640/1982, oxygen is applied to the magnetic layer as energetic particles using an ion gun or a neutral gun in the latter stage of vapor deposition.

b. Glow treatment Q2. N20,02+H20 etc. and Ar.

This method uses an inert gas such as N2, generates plasma by glow discharge, and exposes the surface of the magnetic film to this plasma.

C1 oxidizing gas Items that spray oxidizing gas such as ozone or heated steam.

d. Heat treatment: Oxidation is performed by heating. Heating temperature is 60-1
About 50℃.

2) Wet treatment a, anodization, alkali treatment, C1 acid treatment, chromate treatment, permanganate treatment, phosphate treatment, etc. are used.

d. Oxidizing agent treatment Use N20□ or the like.

It is preferable that a back coat layer be provided directly or via a backing layer on the other surface of the plastic film on which the magnetic layer is not provided.

The backing layer is preferably a thin film of a single metal such as AfL%Cu%W, Mo, Cr, Ti, an alloy of these metals, or an oxide of these metals.

The film thickness of the lining layer formed as necessary is 0.0
It is set to 5 to 1.5 μm.

Further, a back coat layer is provided on the lining layer, which is provided as necessary.

The backcoat layer contains a pigment and a binder of a radiation-curable compound.

Pigments include 1) electrically conductive carbon black and graphite, and 2) 5i02. as an inorganic filler. TiO2, AIl, 2
03, Cr203, SiC, CaO1CaCo3
, zinc oxide, goethite, αFe2O3, talc, kaolin, CaSO4, boron nitride, graphite fluoride, binary acid molybdenum, ZnS, etc. Among them, CaCo3, kaolin, ZnO, goethite, ZnS and carbon are used.

Regarding 1), the amount of such inorganic pigment used is 20 to 100 parts by weight of the binder.
200 parts by weight, and for 2) 10 to 300 parts by weight are suitable; if the amount of inorganic pigment is too large, the coating film will become brittle and dropouts will increase.

The average particle size of the pigment is about 0.01 to 0.3 μm, more preferably 0.02 to 0.1 μm.

The binder of the radiation-curable resin used in the back coat layer is vinyl chloride-vinyl acetate-vinyl alcohol copolymer (including those with carboxylic acid introduced) or acrylic modified vinyl chloride-vinyl acetate-vinyl alcohol copolymer ( (including those into which carboxylic acid has been introduced) and urethane acrylates are preferred.

In addition to the above-mentioned preferred combinations, radiation-curable resins include acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds, which exhibit radically polymerizable unsaturated double bonds, and diallylphthalate. It is possible to use resins containing or introducing into the molecule of a thermoplastic resin a group that can be crosslinked or polymerized by radiation irradiation, such as an allyl double bond or an unsaturated bond such as maleic acid or a maleic acid derivative.

Other usable binder components include monomers such as acrylic acid, methacrylic acid, and acrylamide.

As binders having double bonds, various polyesters, polyols, polyurethanes, etc. can be modified with compounds having acrylic double bonds. Furthermore, by blending a polyhydric alcohol and a polyhydric carboxylic acid as necessary, products of various molecular weights can be produced.

The above-mentioned radiation-sensitive resins are some of them, and these can also be used in combination.

More preferred are: (A) a plastic-like compound with a molecular weight of 5,000 to 0000, which has two or more unsaturated double bonds that are curable by radiation, and (B) a plastic-like compound that has two or more unsaturated double bonds that are curable by radiation. A rubbery compound with a molecular weight of 3,000 to 1 ooooo that has one or more or does not have radiation curability, and (C) a compound with a molecular weight of 200 to 3,000 that has one or more unsaturated double bonds that are curable by radiation. This is a combination in which (A) 20 to 70% by weight, (B) 20 to 80% by weight, and (C) 10 to 40% by weight are used.

As a result, the breaking strength of the coating film is increased, the coating film is strengthened, there is less backcoat abrasion, there is no transfer of inorganic filler powder from the backcoat layer to the magnetic layer, so there is less dropout, and it can be rolled. A magnetic recording medium is obtained which has uniform characteristics in the length direction and is free from curling during curing in a rolled-up form.

In manufacturing the magnetic recording medium of the present invention, if the organic binder is a thermosetting type, the lubricant in the back coat layer is transferred to the magnetic thin film during the manufacturing process, resulting in an output drop due to unstable running as described above. However, this is undesirable because the image no longer appears, or the friction level is still largely insufficient, and the ferromagnetic thin film is removed or destroyed by back-type transfer.

Therefore, for example, it is conceivable to apply a top coat on the magnetic layer first, but this is often inconvenient because it is easily damaged during operation.

Furthermore, in the case of a thermosetting type, the difference in electromagnetic conversion characteristics between the inside and outside of the jumbo roll during thermosetting becomes a problem because of the back-type transition of the backcoat surface due to curling during curing.

On the other hand, in the case of radiation-curable resins, continuous curing is possible due to manufacturing reasons, the curing time is short, there is no back mold transfer as mentioned above, so dropouts can be prevented, and furthermore, radiation curing and top coat treatment can be processed online, which helps to save energy and reduce the number of people involved in manufacturing, leading to cost reductions.

In terms of characteristics, in addition to dropouts caused by the tightness of the magnetic tape during thermosetting, there is no difference in output due to the lengthwise distance of the magnetic tape due to differences in pressure at the inner and outer diameters when it is wound into a roll. .

The unsaturated double bonds in the compounds (A), (B), and (C) are 2 or more, preferably 5 or more for (A), 1 or more for (B), preferably 5 or more for each molecule, ( C) is 1 or more, preferably 3 or more.

The plastic-like compound (A) used in the present invention is one that generates radicals by radiation and produces a crosslinked structure.
It contains two or more unsaturated double bonds in its molecular chain, which can also be obtained by radiation-sensitizing a thermoplastic resin.

Specific examples of radiation-curable resins include acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds, which exhibit radically polymerizable unsaturated double bonds, and allylic double bonds such as diacrylphthalate. A resin that contains or introduces into the molecule of a thermoplastic resin a group that can be crosslinked or polymerized and dried by radiation irradiation, such as a double bond, an unsaturated bond such as maleic acid, or a maleic acid derivative,
Other compounds having unsaturated double bonds that undergo cross-linking polymerization upon radiation irradiation and have a molecular weight of 5,000 to 100,000, preferably 10,000 to 80,000 can be used.

The following unsaturated polyester resins are examples of thermoplastic resins containing groups in their molecules that can be crosslinked or polymerized and dried by radiation irradiation.

A polyester compound containing a radiation-curable unsaturated double bond in the molecule Sn, for example, a saturated polyester resin consisting of an ester bond of a polybasic acid and a polyhydric alcohol as shown in (2) below, in which part of the polybasic acid is maleic acid. Examples include unsaturated polyester resins containing radiation-curable unsaturated double bonds.

The radiation-curable unsaturated polyester resin is prepared by adding maleic acid, fumaric acid, etc. to one or more polybasic acid components and one or more polyhydric alcohol components, in a conventional manner, that is, in the presence of a catalyst.
After dehydration or dealcoholization reaction at 180-200°C under nitrogen atmosphere, the temperature is raised to 240-280°C, and 0.5
It can be obtained by a condensation reaction under reduced pressure of ~1 oonll.

The content of maleic acid, fumaric acid, etc. in the acid component is 1 to 40 mol%, preferably 10 to 30 mol%, in view of crosslinking and radiation curability during production.

Examples of thermoplastic resins that can be modified into radiation-curable resins include the following.

(1) Vinyl chloride copolymer Vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol-vinyl propionate copolymer, vinyl chloride-vinyl acetate-malein Acid copolymer, vinyl chloride-vinyl acetate-terminal OH side chain alkyl group copolymer, such as VROH, V manufactured by UCC Co.
YNC, VYBGX, VERR.

Examples include VYES, VMCA, VAGH, etc., and acrylic double bonds, maleic acid double bonds, and allylic double bonds are introduced into these by the method described later to perform radiation sensitivity modification.

(2) Saturated polyester resin Saturated polybasic acids such as phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, sebacic acid, ethylene glycol, diethylene glycol, glycerin,
Trimethylolpropane, 1.2 propylene glycol, 1.3 butanediol, dipropylene glycol, 1
．． Saturated polyester resins obtained by ester bonding with polyhydric alcohols such as 4-butanediol, 1.6-hexanediol, pentaerythritol, sorbitol, glycerin, neopentyl glycol, 1,4-cyclohexane dimetatool, or polyesters thereof An example is a resin modified with SO-)-N a or the like (for example, Vylon 53S), which is also subjected to radiation sensitivity modification in the same manner.

(3) Polyvinyl alcohol-based resin Polyvinyl alcohol, butyral resin, acetal resin, formal resin and copolymers of these components,
The hydroxyl groups contained in these resins are subjected to radiation sensitivity modification by the method described below.

(4) Epoxy resin, phenoxy resin Epoxy resin produced by the reaction of bisphenol A, nibchlorohydrin, and methyl epichlorohydrin, such as Shell Chemical Co., Ltd. (Epicoat 152° 154.828, 1001, 1004.
1007), Dow Chemicals (DEN431.DER7)
32, DER511, DER331), manufactured by Dainippon Ink Co., Ltd. (Epiclon 400, 800), and phenoxy resin manufactured by UCCfl (P
KHA, PKHC.

P to HH), a copolymer of brominated bisphenol A and epichlorohydrin, and a product manufactured by Dainippon Ink and Chemicals (Evicron 145, 152, 153.1120).

Radiation sensitivity modification is performed using the epoxy groups contained in these resins.

(5) Various types of ja fibril derivatives are used, but the particularly effective ones are nitrified cotton, cellulose acetobutyrate, ethyl cellulose,
Butyl cellulose, acetyl cellulose, etc. are suitable.

Radiation sensitivity modification is performed using the hydroxyl groups in the resin by the method described below.

Other resins that can be used for radiation sensitivity modification include polyfunctional polyester resins, polyether ester resins, polyvinylborolidone resins, and derivatives (pvp
Also effective are acrylic resins containing at least one of olefin copolymers), polyamide resins, polyimide resins, phenol resins, spiroacetal resins, hydroxyl group-containing acrylic esters, and methacrylic esters as polymerization components.

The polymer compound (B) used in the present invention is a thermoplastic elastomer, a prepolymer, or a radiation-sensitive modified version of these, and the latter is more effective.

Examples of elastomers or prepolymers are listed below.

(1) Examples of polyurethane elastomer or prepolymer urethane compounds include incyanate,
2.4-toluene diisocyanate, 2.6-toluene diisocyanate, 1゜3-xylene diisocyanate, 1,4-xylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, 3,3-dimethyl-4,4- Various polyvalent isocyanates such as diphenylmethane diisocyanate, 4.4-diphenylmethane diisocyanate, 3.3-dimethylbiphenylene diisocyanate, 4.4-biphenylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, desmodur, and desmodur N. and linear saturated polyesters (ethylene glycol, diethylene glycol, glycerin, trimethylolpropane,
1.4-butanediol, 1.6-hexanediol,
Polyhydric alcohols such as pentaerythritol, sorbitol, neopentyl glycol, 1,4-cyclohexane dimethinol, and saturated polybasic acids such as phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, and sebacic acid. polyurethane elastomers made of condensates of various polyesters such as linear saturated polyethers (polyethylene glycol, polypropylene glycol, polytetramethylene glycol), caprolactam, hydroxyl-containing acrylic esters, and hydroxyl-containing methacrylic esters. , prepolymers are effective.

It is very effective to modify these urethane elastomers to make them radiation sensitive by reacting their terminal isocyanate groups or hydroxyl groups with monomers having acrylic double bonds or allylic double bonds. .

(2) Acrylonitrile-butadiene copolymer elastomer An acrylonitrile-butadiene copolymer prepolymer with a terminal hydroxyl group, commercially available as PolyBD Retired Resin manufactured by Sinclair Vetro Chemical Co., Ltd., or an elastomer such as Hiker 1432J manufactured by Nippon Zeon Co., Ltd., is particularly suitable for butadiene. The double bonds therein generate radicals by radiation, making it suitable as a nylon tor component for crosslinking and polymerization.

(3) Polybutadiene elastomer A prepolymer having a low molecular weight terminal hydroxyl group such as PolyBD Retired Resin R-15 manufactured by Sinclair Vetrochemical Co., Ltd. is particularly suitable in terms of compatibility with thermoplasticity.

Since R-15 prepolymer has a hydroxyl group at the end of the molecule, it is possible to increase radiation sensitivity by adding an acrylic unsaturated double bond to the end of the molecule, making it even more advantageous as a binder. .

In addition, polybutadiene cyclized product, CBR manufactured by Japan Synthetic Rubber Co., Ltd.
-M901 also has excellent properties due to its combination with thermoplastic resin.

Other suitable thermoplastic elastomer and prepolymer systems include styrene-butadiene rubber, chlorinated rubber, acrylic rubber, isoprene rubber, and its cyclized product (ClR701 manufactured by Nippon Gosei Rubber Co., Ltd.); Elastomers such as plasticized saturated linear polyester (Toyobo Vylon #300) can also be effectively used by subjecting them to the radiation-sensitizing treatment described below.

(C) Compounds having a radiation-curable unsaturated double bond used in the present invention include styrene, ethyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate,
Diethylene glycol acrylate, diethylene glycol dimethacrylate, 1,6-hexane glycol diacrylate, 1,6-hexane glycol diacrylate, trimethylolpropane trimethacrylate, polyfunctional oligoester acrylate (Aloex M-7
100, Toagosei), acrylic modified products of Tuborane 4040) in urethane elastomers, and products in which functional groups such as C0OH are introduced into these products.

It is known that some polymers disintegrate when irradiated with radiation, while others cause crosslinking between molecules.

Examples of substances that cause crosslinking between molecules include triethylene, polypropylene, polystyrene, polyacrylic ester,
polyacrylamide, polyvinyl chloride, polyester,
There are polyvinylpyrrolidone rubber, polyvinyl alcohol, and polystyrene.

With such crosslinked polymers, the crosslinking reaction occurs even without the above-mentioned modification, so in addition to the modified products mentioned above, these resins can be used as they are as backcoat resins for radiation crosslinking. be.

Furthermore, according to this method, even a solvent-free resin that does not use a solvent can be cured in a short time, so such a resin can be used for a back coat.

Particularly preferable combinations of the radiation-curable resin composition used in the present invention include a vinyl chloride-vinyl acetate copolymer in which the compound (A) is partially saponified, and a vinyl chloride-vinyl acetate copolymer in which a carboxylic acid is introduced. It is a compound obtained by reacting a compound having an isocyanate group obtained by reacting a copolymer or phenoxy resin with a polyisocyanate compound, and an acrylic compound or a methacrylic compound having a functional group that is reactive with the isocyanate group. The compound (B) is a compound obtained by reacting an isocyanate compound or polyol (polyurethane elastomer) with an acrylic compound or methacrylic compound having a reactive functional group, which is obtained by reacting a polyol with an isocyanate compound. , (C) is a polyfunctional (meth)acrylate monomer, oligoester acrylate, or (B) is a low molecular weight compound.

The thickness of such a back coat layer is 0.2 to 2.5 μm.
The thickness is more preferably about 0.3 to 1.5 μm. If the film thickness is less than 0.2 μm, sufficient running stability cannot be obtained, and if it exceeds 2.5 μm, the back coat layer may become scratched.

In addition to the pigments and organic binders described above, the back coat layer may contain various known additives such as lubricants, if necessary.

As a coating solvent, ME, cyclohexanone, MIB
Ketones such as K, alcohols such as IPA, aromatics such as toluene, and halogens such as dichloroethane are used.

When using, one of these types may be used alone, or two types may be used together.
More than one type may be used in combination, or any one of them may be used.

As lubricants (including dispersants), any of the types conventionally used for this type of back coat layer can be used, including caprylic acid, capric acid, lauric acid, myristic acid,
Valmitic acid, stearic acid, behenic acid, oleic acid,
Fatty acids with 12 or more carbon atoms such as elaidic acid, linoleic acid, lylunic acid, stearolic acid (RCoO) (I, R is an alkyl group with 11 or more carbon atoms): Alkali metals (Li, Na) of the above fatty acids.

K, etc.) or alkaline earth metals (Mg, Ca.

Metal soap consisting of Ba, etc.); lecithin etc. are used.

In addition, higher alcohols having 12 or more carbon atoms, sulfuric esters thereof, surfactants, titanium coupling agents, silane coupling agents, etc. can also be used.

These lubricants (dispersants) are added in an amount of 1 to 20 parts by weight per 100 parts by weight of the binder.

In addition to the above, examples of lubricants include silicone oil, graphite, molybdenum disulfide, tungsten disulfide, monobasic fatty acids with 12 to 16 carbon atoms, and monobasic fatty acids with 3 to 12 carbon atoms.
Fatty acid esters consisting of alcohols, carbon number 17
A fatty acid ester or the like is used, which is composed of m or more monobasic fatty acids and m alcohols having 21 to 23 carbon atoms in total, including the total number of carbon atoms in the fatty acid.

These lubricants contain 0.00 parts by weight per 100 parts by weight of binder.
It is added in an amount of 2 to 20 parts by weight.

In addition, as other additives, anything used in this type of back coat can be used, but for example, as an antistatic agent, natural surfactants such as saponin, alkylene oxide type, glycerin type, glycidol. Nonionic surfactants such as
Quaternary ammonium salts, pyridine and other heterocycles,
Cationic surfactants such as phosphonium or sulfoniums; Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester groups, phosphoric ester groups; sulfuric acid of amino acids, aminosulfonic acids, amino alcohols; Amphoteric activators such as phosphoric acid esters are used.

Further, as the lubricant, antioxidant, etc. contained in the back coat layer or the top coat layer described below, radiation-curable ones are preferable.

In such cases, the active energy rays used for crosslinking include electron beams using a radiation accelerator as a source, C060
γ-rays using 5r90 as a radiation source, β-rays using 5r90 as a radiation source,
xi or ultraviolet light using a radiation source as a radiation source is used.

In particular, as an irradiation source, it is advantageous to use radiation using a radiation accelerator from the viewpoint of controlling the absorbed dose, introducing it into the manufacturing process line, blocking ionizing radiation, etc.

The radiation characteristics used when curing the above-mentioned back coat layer and the below-mentioned top coat layer include an acceleration voltage of 100 to 750 V, preferably 150 to
Using a 300Kv radiation accelerator, the absorption ram is 0.5
It is convenient to irradiate to ~20 megarads.

For the radiation curing mentioned above, a low-dose type radiation accelerator (manufactured by Energy Sciences, Inc. in the United States)
Electrocurtain system) etc. are extremely advantageous for introducing into the tape coating processing line, blocking secondary X-rays inside the accelerator, etc.

Alternatively, a van de Graaf type accelerator, which has been widely used as a radiation accelerating material, may be used.

In addition, during radiation crosslinking, it is important to irradiate the back coat layer and top coat layer with radiation in an inert gas stream such as N2 gas or He gas, and irradiation in air is not suitable for binder components. When crosslinking, the shadow M such as 03 caused by radiation irradiation prevents radicals generated in the polymer from working advantageously in the crosslinking reaction, which is extremely disadvantageous.

Therefore, the atmosphere in the area where the active energy rays are irradiated is N2. He, Co
It is important to maintain an inert gas atmosphere such as □.

Further, it is preferable that the surface of the base or backing layer on which the back coat layer is provided be subjected to plasma treatment for the purpose of improving adhesive strength. Such plasma processing is usually performed using an inorganic gas as a processing gas, and among these processing gases, it is particularly preferable to use a processing gas containing O, N, and H.

There is no particular restriction on the frequency of plasma treatment.

Such plasma treatment improves the adhesive strength between the backing layer and the backcoat layer.

It is preferable to further provide a top coat layer on the magnetic layer of the magnetic recording medium as described above.

The top coat layer contains a compound having a fatty acid ester, a group having a radiation-sensitive unsaturated double bond, and a fluorine-substituted alkyl group.

The physical properties of the fatty acid ester contained in the top coat layer include a melting point of -20 to 30°C, more preferably -10 to 30°C.
It is preferable to use one at 25°C.

Therefore, fatty acid esters having such physical properties include, for example, monobasic fatty acids with 4 to 24 carbon atoms such as 1, capric acid, lauric acid, myristic acid, valmitic acid, stearic acid, and arachidic acid, and monobasic fatty acids with 1 to 24 carbon atoms. Among these, fatty acid esters having a total of 7 to 26 carbon atoms consisting of a monobasic fatty acid with 6 to 20 carbon atoms and a monovalent saturated alcohol are particularly preferable. .

Generally, one type of fatty acid ester is used as the fatty acid ester contained in the top coat layer, but two or more types may be mixed and used as necessary.

Further, the top coat layer contains a compound having a group having a radiation-sensitive unsaturated double bond and a fluorine-substituted alkyl group.

In this case, the group having a radiation-sensitive unsaturated double bond is preferably a group represented by CH2=CR2-Co- (R2 represents a hydrogen atom or an alkyl group).

In addition, the fluorine-substituted alkyl group has 2 carbon atoms.
~20 alkyl groups, in which a plurality of hydrogen atoms are replaced with fluorine atoms. Among these, those represented by CnF 2 n + +- (n is an integer from 2 to 20) are particularly preferred.

As such a compound, a compound represented by the following formula (I) or (II) is particularly preferable.

Formula (I) 1 (Formula (■)) (In the above formulas (I) and (Il), R1 is a fluorine-substituted alkyl group, Ll and L2 each represent two linking groups, and R2 represents a hydrogen atom or an alkyl group. , m is 1 or 2.) In the above formulas (I) and (n), R3 preferably represents a fluorine-substituted alkyl group having 2 to 2 o carbon atoms,
In particular, a group represented by Cn F 2n+1- (n is 2 to 2
o integer) is preferable, for example, C4F9, CsF
z, C6F13, C? F15, C6F14, C9F+9
, CIOF 21, etc. are suitable.

LI and L2 are each substituted or unsubstituted alkylene group or arylene group, or a group bonded thereto, or -〇-1-S-1-SO□-
1-Co-1-CoO-1-OCo-1 each substituted or unsubstituted -NH-1-S 02 NH-1-NH
A group to which SO2-1-CoNH-1-NHCo- or the like is bonded is preferable. Among these, in particular, the number of carbon atoms is 1 to
4, an unsubstituted alkylene group, etc. are preferred.

Note that these Ll and L2 may be the same or different.

In addition, L I , t, 2 may further include other substituents, such as an alkyl group, an aryl group, a hydroxy group, and furthermore, C
It may be substituted with H2=CR2Coo-L'- group, etc.

R2 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and a single hydrogen atom or a methyl group is particularly preferred.

Further, m is 1 or 2.

Specific examples of the compounds represented by formula (I) and formula (11) are listed below.

FI O F2 0 Otori Cs, F17C2H4-0-C-CHgiCH2F3
Such compounds can be easily produced using known methods.

To give an example, R1 in formula (1) and formula (n)
A halogenated compound having Cn F 2n+1 groups, e.g. ca FI7-c2H41, is reacted with water to form the corresponding alcohol, e.g. c, F17-C2H4-O
Make H. This alcohol can be subjected to a condensation reaction with an unsaturated acid, such as acrylic acid, using a strong acid as a catalyst to obtain a desired compound, such as ca FI7-C2H4-0-C-CH=CH2.

As for the compounds represented by the formula (I) and the formula (■), the IMA of the compound of the formula (I) or the formula (11) may be used alone, or two or more thereof may be used in an appropriate mixture. Often, the total amount is 200 parts by weight or less, more preferably 10 to 100 parts by weight, per 100 parts by weight of fatty acid ester.
It is considered to be a melon. Outside this range, problems such as clogging, sharpness, and increased jitter occur.

By using a compound having a radiation-sensitive unsaturated double bond in such a top coat layer, the adhesive strength with the magnetic layer is improved, and therefore the durability is improved. The top coat layer is rapidly bonded to the magnetic layer, preferably by irradiating with activation energy rays to cause a crosslinking reaction.
Durability is further improved. Further, the top coat layer has particularly excellent running stability by using, for example, a compound having a fluorine-substituted alkyl group represented by CnF2n or + (n is an integer between 2 and 20).

n of C n F 2n + I in radiation sensitive compound
If n exceeds 20, the overall strength of the top coat layer to the magnetic layer will be weakened, and if n is less than 2, the lubricity will drop significantly, which is not preferred.

Furthermore, by using a compound having both a radiation-sensitive unsaturated double bond and a fluorine-substituted alkyl group represented by, for example, C1F 2n+I, in the above-mentioned top coat layer, the runnability is greatly improved, and it is possible to prevent scratches and head. No clogging occurs.

A top coat layer containing such compositional components is usually formed using gravure coating, reverse roll coating, air knife coating, air doctor coating, etc.
γ-rays using 5r90 as a radiation source, β-rays using 5r90 as a radiation source,
It is cured by irradiation with activation energy rays such as X-rays or ultraviolet rays using a ray generator as a ray source. The irradiation amount is 0
．． A range of 5 to 20 Mrad is preferred.

As the coating solvent, as in the case of the back coat layer described above, a ketone type such as MEK, cyclohexanone, or MIBK, an alcohol type such as Natsu PA, an aromatic type such as toluene, a halogen type such as dichloroethane, etc. are used.

When used, one of these types may be used alone, or two or more types may be used in combination.

The above-mentioned top coat layer may further contain various known lubricants, antioxidants, curing agents, etc., if necessary.

As the lubricant, lubricants conventionally used for magnetic recording media such as silicone oil, fluorine oil,
Alcohols, fatty acids, paraffin, liquid paraffin, surfactants, etc. can be used, but fatty acids are particularly preferred.

Fatty acids include fatty acids with 12 or more carbon atoms (RCoOH,
R is an alkyl group having 11 or more carbon atoms), for example, caprylic acid, capric acid, lauric acid, myristic acid, valmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, lilunic acid, stearolic acid, etc. preferable.

The silicone oil used is one made of fatty acid denatured or partially fluorine denatured. The alcohol used is one made of higher alcohol, and the fluorine oil used is one obtained by electrolytic substitution, telomerization, oligomerization, etc.

Furthermore, a radiation curing type lubricant can be suitably used. When a radiation-curing lubricant is used, the transfer of the lubricant to the back mold is suppressed, which prevents dropouts, differences in output depending on the inner and outer diameters when wound into a roll, as well as online Advantages such as the possibility of manufacturing on top of the product arise.

As radiation-curable lubricants, compounds having a molecular chain ζ acrylic double bond exhibiting lubricity in their molecules, such as acrylic esters, methacrylic esters, vinyl acetate esters, acrylic amide compounds, and vinyl alcohol esters are used. , methyl vinyl alcohol ester, allyl alcohol ester, chrycerite, etc.
The structural formula of lVI lubricant is CH2=CH-CH2C
0OR.

CH2=CHC0NHCH20CoR1CH20CoR RCoOCH=CH2, etc. (wherein, R is a straight 2n or branched saturated or unsaturated hydrocarbon group, and the number of carbon atoms is 7 or more, preferably 12 or more and 23 or less, and these are fluorine-substituted and ).

Preferred specific examples of these radiation-curing lubricants include:
Examples include stearic acid methacrylate (acrylate), stearyl alcohol methacrylate (acrylate), glycerin methacrylate (acrylate), glycol methacrylate (acrylate), and silicone methacrylate (acrylate).

As the active energy ray used for crosslinking the radiation-curable additive used in the above-mentioned top coat layer, an electron beam using a radiation accelerator as a radiation source, C.

60! ! i! The γ-ray source, 5r90f! Examples include β-rays using a zero-ray source, X-rays using an X-ray generator as a source, or ultraviolet rays. In particular, as an irradiation source, it is advantageous to use radiation generated by a radiation accelerator from the viewpoint of controlling absorption radiation (1), introducing it into a manufacturing process line, and shielding ionizing radiation.

The thickness of the top coat layer is preferably 5 to 200 layers.

If it is too thick, it will not hold its shape well or it will scratch. Also, if it is too thin, clogging will occur.
Since the surface roughness of the magnetic layer without a top coat is preferably 100 Å or less, it has been found that when a top coat layer is formed thereon, if it is too thick, scratches may occur.

If it is too small, the adsorption of the top coat layer will be too weak.
It is expected that clogging will occur. A particularly preferable range is 10 to 100 people.

Note that the top coat may be formed by plasma polymerization.

When forming the above-mentioned top coat, as mentioned above, commonly used antioxidants, curing agents, etc. can be further added in commonly used amounts.

When a curing agent is used in the present invention, radiation-curable polymers and oligomers are suitable as the curing agent.
Compounds with a molecular weight of less than 12,000 are used as radiation-curable monomers, and compounds with molecular weights of 500 to 10, as oligomers are used.
000 is used. These are styrene, ethyl acrylate, ethylene glycol diacrylate,
Ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, l.

Includes 6-hexane glycol diacrylate, 1゜6-hexane glycol diacrylate, etc., and particularly preferably includes the following = N-vinylpyrrolidone, pentaerythritol tetraacrylate (methacrylate),
Pentaerythritol triacrylate (methacrylate), trimethylolpropane triacrylate (methacrylate), trimethylolpropane diacrylate (methacrylate), polyfunctional oligoester acrylate (Toagosei Co., Ltd. Aronix M-7100, M-
5400, 5500, 5700, etc.) Urethane elastomers, acrylic modified products of Tuboran 4040), or functional groups such as C0OH introduced into these urethane elastomers, phenol ethylene oxide adduct acrylates (methacrylatenes, represented by the general formula below) Compounds with an acrylic group (methacrylic group) or ε-caprolactone-acrylic group attached to a pentaerythritol condensed ring: and special acrylates represented by the following general formula: (CH2=CHC0OH2)3-CCH20H: (CH
2=CHC0OH2)3-CCH2CH3.

(n=1-6) CH2=CHCoO-(CH2CH20)4-CoCH
=CH2; A Niacrylic acid; C
Examples include those into which a functional group such as 0OH is introduced.

(In the formula, R,, R2: alkyl group, n: integer) When adding a lubricant, an antioxidant, a curing agent, etc. to the top coat layer in the present invention, the total weight of these is determined by the formula (I) and the formula ( It is preferable that the amount is within 10 times the total weight of the compound having one or more radiation-sensitive unsaturated double bonds as represented by n) and having a fluorine-substituted alkyl group. Further, it is preferable that the weight of the antioxidant does not exceed the weight of the lubricant sand hardener.

Note that various undercoat treatments may be applied to the plastic film, and an underlayer may be further formed between the plastic film and the magnetic layer or backing layer.

Further, fine protrusions may be provided at a predetermined density on the surface of the magnetic recording medium of the present invention.

The fine protrusions are 30 to 300 people, more preferably 50 to 300 people.
It has a height of 250 people.

That is, the above protrusions cannot be observed with an optical microscope and measured with a stylus type surface roughness meter, but can be observed with a scanning electron microscope.

If the height of the protrusions exceeds 300 and becomes observable with an optical microscope, the electromagnetic conversion characteristics deteriorate and the running stability deteriorates.

Furthermore, if the number of participants is less than 30, there is no effective improvement in physical properties.

And the density is more than 105 pieces per 1 mm2 on average.
More preferably 10'' to 109 pieces, especially 106 to 10 pieces
There are 8 pieces.

When the protrusion density is less than 10 5 /mm 2 , noise increases, still characteristics deteriorate, and other physical properties deteriorate, making it unsuitable for practical use.

Moreover, if the number exceeds 109 pieces/m2, the effect on physical properties will decrease.

Note that the diameter of the projection is generally about 200 to 1000 people.

In order to provide such protrusions, it is usually sufficient to arrange fine particles on the substrate. What is the particle size?

The number may be 30 to 1,000, and thereby fine protrusions corresponding to the particle size are formed.

The fine particles used are usually those known as colloidal particles, such as Sio2 (colloidal silica), 8! 203 (alumina sol), Mgo%Ti
e,, ZnO1Fe203, zirconia, CdolNi
o%CaWO4, CaC0, BaCo3, Coco, BaTiO3, Ti (titanium black), Au, Ag, Cu, Ni, Fe, various hydrosils, resin particles, etc. can be used. In this case, it is particularly preferable to use inorganic substances.

Such fine particles may be prepared by forming a coating solution using various solvents, applying this onto a substrate, and drying it, or by applying a coating solution containing a resin component such as various aqueous emulsions and drying it. Good too.

Note that, in some cases, these coating liquids may be provided as a top coat layer on the magnetic thin film layer instead of being provided on the substrate.

Furthermore, when a resin component is used, it is also possible to provide gentle protrusions based on these fine particles, superimposing them on the fine protrusions, but it is usually not necessary to do so.

If necessary, a non-magnetic metal thin film layer may be interposed between the top and bottom ferromagnetic metal thin film layers.

(2) Specific Effects of the Invention According to the present invention, since the magnetic layer has a structure of two or more layers, the length of the magnetic columnar crystal grains becomes small, so that the film strength of the magnetic layer is improved. Therefore, the running stability is extremely high, and the occurrence of cracks in the magnetic layer and scratching of the magnetic surface due to running is extremely small, and the amount of head PJ edges and dropouts are also extremely small.

Furthermore, since the magnetic layer contains carbon in the form of an organic polymer, there is almost no curling or cupping of the medium, resulting in stable output and improved corrosion resistance and running durability.

(2) Specific Examples of the Invention Hereinafter, specific examples of the present invention will be shown and the present invention will be explained in more detail.

(Example 1) A polyester (PET) film having the thickness shown in Table 1 below was moved along the circumferential surface of a cylindrical cooling can.
An alloy of Co80 and Ni20 (weight ratio) was melted and deposited obliquely in a chamber in which +Ar (volume ratio 1:1) was flowed at a rate of 800 cc per minute and the vacuum was set to 1 ox l O-' Torr. Co-Ni shown in Figure 1 by
A two-layer thin film of -0 was formed. In addition, prior to vapor deposition,
The film surface was plasma treated.

The processing conditions were: processing gas Ar, gas flow rate 100 r for 117 minutes, degree of vacuum 0.05 Torr, electric current f 150 kHz, 200
It was set as W.

Table 1 shows the minimum incident angle of the deposited material and the thickness of the magnetic layer.

For comparison, a single-layer Co--Ni-0 thin film having a thickness of 0.15 μm was formed by diagonal evaporation only at the portion at the incident angle of 30° to 90°.

Incidentally, the vapor deposition was carried out while introducing a predetermined amount of C and H4 gases as introduced organic substances into the vacuum chamber.

After the organic matter was incorporated into the magnetic layer in this manner, the organic matter in the magnetic layer was polymerized by passing through a plasma treatment vacuum chamber in the next step.

Plasma treatment The plasma treatment conditions in the vacuum chamber were as follows: chamber pressure 0.0 I Torr, RF 13.56 MHz, 500
W and plasma treated with Ar.

The average carbon/metal ratio in the magnetic layer was determined by measuring the profile of each composition in the thickness direction by Ausch spectroscopy or SIMS analysis while performing ion etching, and calculating the average carbon/metal ratio in the magnetic layer. In this measurement, we first measured the standard sample cobalt carbide C02C, determined its measurement sensitivity, and calculated C/C.

It was determined by (count number of Co) x (measurement sensitivity of Co).

Further, for Ni etc., the sensitivity ratio with Co was calculated as a correction factor.

Note that a large amount of oxygen was unevenly distributed at the interface between the lower layer and the upper layer and on the surface opposite to the base. Furthermore, the surface opposite to the base was covered almost exclusively with oxide.

Hc = 1000 0e, and the average amount of oxygen in the film was 40% at the atomic ratio of Co to Ni (-1π--x100) oN t For each piece shown in Table 1, ion etching was performed with Ar. However, O/(
Co or Co+N i ) atomic ratio, C+ (surface), c+'' (upper layer average), C2 (interface with lower layer substrate)
, C2'' (lower layer average), and C3 (near the interface between the lower layer and the upper layer) are also written.

After the back surface of this film was subjected to plasma treatment, a back coat layer as shown below was formed.

Note that the plasma processing conditions include 02 gas as the processing gas,
The gas flow rate was 100 m/min, the degree of vacuum was 0.5 Torr, the power source was 50 Hz, 200 W, and the film running speed was 30 m/min.

Further, if necessary, a top coat layer as shown below was provided on the magnetic layer. The thickness of these layers was as shown in Table 1.

(1) Formation of back coat layer Mr. Kokyu Uni 1 Part by weight Carbon black 7Si02
2 Acrylic modified vinyl chloride
Vinyl acetate-vinyl alcohol copolymer 30
Acrylic modified polyurethane elastomer 10 Acrylic ester oligomer 4 Dispersion aid
0.4 The above mixture was dispersed in a ball mill for 5 hours to form a dry thickness of 1 on the plasma treated backing layer.
-, using an electrocurtain type electron beam accelerator at an acceleration voltage of 150 KeV and an electrode current of 1.
The back coat layer was irradiated with an electron beam in N2 gas at 0 mA and an absorbed dose of 5 Mrad.

(2) Formation of top coat layer A composition as shown below was formed on the magnetic layer.

Tubucoat y Part by weight Butyl myristate m, p, = 1.0°C 0.5F-2 (compound in the above specific example) 0.3ME
30 and cyclohexanone and 70 were stirred and mixed at room temperature for 1 hour, and the resulting mixture was gravure coated onto the above magnetic coating surface to a uniform thickness, and dried at 100° C. for 1 minute.

The following measurements were performed on each of the samples shown in Table 1 below formed in this manner. Note that the medium traveling direction and the direction of inclination of the magnetic crystal grains with respect to the normal to the underlying substrate were made to be the same direction.

(1) Cupping A 1/2" wide slit was made and the height of the cupping was measured.

(2) Electromagnetic conversion characteristics Outputs at center frequencies of 0.75 MHz and 5 MHz were measured, and values were determined in OdB, which is the output of sample NO68.

Deck used: 5ONY A-300 Head: Sputter Sendust mode: SP mode (3) Still durability The time required for the output to decrease by 5 dB under the condition of a temperature of 0° C. was determined.

Deck used: 5ONY A-300 (Used with still release mechanism removed) Head varnish grasshopper Sendust (4) Corrosion resistance Each sample was left at 60℃ and 90% relative humidity for 7 days, and -△φm/cm2 φm (%) was measured.

These results are shown in Table 2.

(Example 2) A magnetic layer was formed by the same method as in Example 1, except that the minimum incident angle of the vapor deposited substance and the 0/(Co or Co+N i ) atomic ratio in the magnetic layer were as shown in Table 3. The samples shown in Table 3 were prepared using the same back coat layer and traboot layer as in Example 1. (Sample No.

11-22).

The same measurements as in Example 1 were carried out for each sample thus formed. In addition, the electromagnetic conversion characteristics were calculated using the output of sample No. 22 as OdB.

The results are shown in Table 4.

(Example 3) A magnetic layer was formed by the same method as in Example 1, except that the base thickness and the upper and lower layer thicknesses of the magnetic layer were as shown in Table 5, and the same back coat layer as in Example 1 was used. The samples shown in Table 5 were prepared using the Traputo layer. (
Sample No. 31-38).

The same measurements as in Example 1 were performed for each sample formed in this way. Note that the electromagnetic conversion characteristics were determined by taking the output of sample No. 38 as OdB.

The results are shown in Table 6.

In addition, sample No. 31, 32, 3 for the output of sample No. 37 (base thickness 7, magnetic layer configuration: single layer)
The improvement in output of 3.36 (base thickness: 7 layers, magnetic layer configuration: 2 layers) is shown in Table 6.

From the results shown in Tables 1 to 6, the effects of the present invention are clear.

That is, it is clear that the sample having the magnetic layer structure of the present invention provides good values in all of the measurement items.

In addition, when the base thickness is 8 μm or less, when the ratio of the upper layer thickness to the lower layer thickness is 0.2 to 0.9, extremely high improvements in 5 MHz output and durability can be seen, and the 5 MHz output can withstand practical use. It can be seen that even with a thin base thickness, it exhibits sufficient electromagnetic conversion characteristics and durability for practical use.

Further, colloidal silica was coated on a polyester film subjected to plasma treatment to obtain a substrate having microprotrusions, and a sample was prepared in the same manner as in the above-mentioned example.

The diameter of the microprotrusions on the surface of the magnetic layer of this sample was 250, and the density of microprotrusions was 5×10′/llI2.

In this sample, the amount of head adhesion during high-temperature running decreased.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a cross section parallel to the medium direction of one embodiment of the magnetic recording medium of the present invention. FIG. 2 is a schematic diagram of a cross section parallel to the medium direction of another embodiment of the magnetic recording medium of the present invention. FIG. 3 is a schematic diagram of the vapor deposition apparatus. FIG. 4 is a schematic diagram of the plasma processing apparatus. Explanation of symbols! ...magnetic recording medium, 2..substrate, 3.. lower layer of ferromagnetic metal thin film, 4.. upper layer of ferromagnetic metal thin film, 5.. lower layer crystal grain, 6. ...upper layer crystal grain, arrow a...medium length direction, 7...top coat layer, 8...back coat layer, 11...evaporation device, 12...winding Output roll, 13... Base, 14... Cooling drum, 15... Nozzle, 16... Evaporation source, 17... Shielding plate, 20... Polymerization processing device, 21.22...processing gas source, 23.24...mass flow controller, 25...
...Mixer, 26...DC, AC and variable frequency power supply, 27
．． 57...Electrode, 30...Take-up roll, 31...Take-out roll, 111...Liquid nitrogen trap, 112...Oil rotary pump applicant TDC Co., Ltd. - τ ;-f7: Agent Patent attorney Yo Ishii -(“・-fFIG
,1 FIG,3 ]1

Claims (6)

[Claims] (1) A ferromagnetic metal thin film layer mainly composed of Co is provided on a plastic film substrate, and this ferromagnetic metal thin film layer has two
1. A magnetic recording medium having a multilayer structure consisting of more than one layer, wherein at least one of the ferromagnetic metal thin film layers contains carbon. (2) The carbon/metal atomic ratio of the layer containing carbon is 10^-^
8 to 10^-^2. The magnetic recording medium according to claim 1. (3) Claim 1, wherein the ferromagnetic metal thin film layer has an overall carbon/metal atomic ratio of 10^-^8 to 10^-^2.
The magnetic recording medium according to item 1 or 2. (4) When the ferromagnetic metal thin film layer is deposited, the minimum incident angle of the deposited substance with respect to the normal to the substrate is 50° when the lowest layer is placed on the substrate side.
The magnetic recording medium according to any one of claims 1 to 3, wherein the angle is 20° to 90° when the uppermost layer is formed on the side opposite to the substrate. (5) A patent claim in which the value C_2/C_1 obtained by dividing the oxygen concentration C_2 near the interface on the substrate side of the bottom layer of the ferromagnetic metal thin film layer by the oxygen concentration C_1 near the surface of the top layer opposite to the substrate is 0.3 or less The magnetic recording medium according to any one of items 1 to 4. (6) The value C_3/C_1 obtained by dividing the oxygen concentration C_3 near the interface with the top layer of the layer adjacent to the top layer by the oxygen concentration C_1 near the surface of the top layer opposite to the substrate is 0.1 to 3. 0
A magnetic recording medium according to any one of claims 1 to 5.